Roughly chop the chocolate . Keep aside.
Beat or cream the butter with the sugar and salt using an electric mixer until smooth.
Beat in the egg and the vanilla .
Whisk together the flour and baking powder.
Add the flour mixture and mix until just combined.
Fold in the chopped chocolate.
Shape the dough into one or two logs , wrap in clingfilm and chill for atleast two hours.
Meanwhile , preheat your oven to 180 C/ 350 F . Line a baking sheet with parchment or grease well.
After chilling period, unwrap the cookie dough logs and slice cookies of about 1 cm thickness.
Place cookies on the prepared baking sheet , about 2 inches apart and adjust the shape if needed.
Bake at 180 c/ 350 F for 10 minutes , turn the baking sheet front backwards , bake for 8-10 more minutes until lightly brown on the edges.
Cool on pan for two minutes and then completely on wire rack.